This invention relates to measurement of radioactive rays, and more particularly to a method of manufacturing a radioactive ray measuring device by which the amount or dose of irradiated radioactive rays can be easily measured at a high precision.
It is very important to measure the dose of irradiated radioactive rays in the products, materials, etc. which may be subjected to radioactive rays in various radioactive ray irradiating facilities, such as atomic furnaces, nuclear fusion furnaces, and all the facilities which emit radioactive rays.
Conventionally, many kinds of dosimeter have been developed and utilized. These dosimeters which are often used in recent years include alanine dosimeter, CTA dosimeter, radiochromic dosimeter, etc.
In the alanine dosimeter, non-paired electrons which are produced by irradiating radioactive rays on alanine specimen are measured by electron spin resonance (ESR). Thus, an ESR system which is expensive and large, is necessary. Further, for achieving accurate dose measurement, uniform specimens of controlled density, etc. are necessary. Also, it is necessary for the measuring ESR system to have a uniform magnetic field. Usually, high precision among specimens cannot be expected without using the same ESR system. It is difficult to perform highly accurate dose measurement by using the alanine dosimeter. Much efforts will be required to achieve precise measurements by using the alanine dosimeter.
In CTA dosimeter, radioactive rays are irradiated on a cellulose acetate specimen and light absorption in the irradiated cellulose acetate specimen, appearing in ultra violet region is measured. Thus, a spectrometer of ultra violet region is necessary. Further, since the subject absorption is in the ultra violet region, the measurement is sensitive to stain of grease, oil, etc. Special care should be paid for the handling of specimens and measuring tools. Yet further, since the spectrum in the measurement wavelength region does not exhibit isolated peaks, the reading of measured absorption is apt to be inaccurate. The range of measurable dose is at most 150 kGy.
In a radiochromic dosimeter, radioactive rays are irradiated to a nylon specimen added with about 30% of dye, and then the absorption bands appearing around 600 nm and 510 nm are measured. This radiochromic dosimeter also responds to light rays. Therefore, the read can vary largely depending on how for light rays are shielded. Further, the read can also vary depending on the humidity. In such way, this dosimeter is inconvenient in handling. The measurable dose range of this dosimeter is up to 30 kGy. However, relatively good precision can be obtained by paying sufficient attentions.
When using a CTA or radio chromic dosimeter, an accurate dose cannot be measured until at least one day has elapsed after the irradiation. Also the dose cannot be known unless the specimen is taken out after the irradiation and is measured by a separate instrument.